Three dimensional imaging utilizing stacked imager devices and associated methods

ABSTRACT

Stacked imager devices that can determine distance and generate three dimensional representations of a subject and associated methods are provided. In one aspect, an imaging system can include a first imager array having a first light incident surface and a second imager array having a second light incident surface. The second imager array can be coupled to the first imager array at a surface that is opposite the first light incident surface, with the second light incident surface being oriented toward the first imager array and at least substantially uniformly spaced. The system can also include a system lens positioned to direct incident light along an optical pathway onto the first light incident surface. The first imager array is operable to detect a first portion of the light passing along the optical pathway and to pass through a second portion of the light, where the second imager array is operable to detect at least a part of the second portion of light.

PRIORITY DATA

This application claims the benefit of priority as a continuationapplication to U.S. patent application Ser. No. 14/206,890, filed onMar. 12, 2014, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/798,805, filed on Mar. 15, 2013, each of whichis incorporated herein by reference in their entireties.

BACKGROUND

Active pixel sensors (APS) are image sensors including integratedcircuit containing an array of pixel sensors, each pixel containing aphotodetector and an active amplifier. Such an image sensor is typicallyproduced by a complementary metal-oxide-semiconductor (CMOS) process.CMOS APS can be used in web cams, high speed and motion capture cameras,digital radiography, endoscopy cameras, DSLRs, cell phone cameras, andthe like. Other advances in image sensor technology have beenimplemented, such as the use of an intra-pixel charge transfer alongwith an in-pixel amplifier to achieve true correlated double sampling(CDS) and low temporal noise operation, and on-chip circuits forfixed-pattern noise reduction.

Some CMOS APS imagers have utilized backside illuminated (BSI)technology. BSI imager technology includes a semiconductor wafer bondedto a permanent carrier on the front side and then thinned from thebackside. Passivation layers, anti-reflecting layers, color filters andmicro-lens can be positioned on the backside, and the resulting devicecan be backside illuminated. Through-Silicon Vias (TSV) can be used toprovide electrical connections from the front side to backside outputpads. BSI CMOS APS imagers are becoming useful technology for many typesof visible imagers in cell phones and digital cameras.

More generally, electromagnetic radiation can be present across a broadwavelength range, including visible range wavelengths (approximately 350nm to 800 nm) and non-visible wavelengths (longer than about 800 nm orshorter than 350 nm). The infrared spectrum is often described asincluding a near infrared portion of the spectrum including wavelengthsof approximately 800 to 1300 nm, a short wave infrared portion of thespectrum including wavelengths of approximately 1300 nm to 3micrometers, and a mid to long range wave infrared (or thermal infrared)portion of the spectrum including wavelengths greater than about 3micrometers up to about 20 micrometers. These are generally andcollectively referred to herein as infrared portions of theelectromagnetic spectrum unless otherwise noted.

Traditional silicon photodetecting imagers have limited lightabsorption/detection properties. For example, such silicon baseddetectors are mostly transparent to infrared light. While other mostlyopaque materials (e.g. InGaAs) can be used to detect infraredelectromagnetic radiation having wavelengths greater that about 1000 nm,silicon is still commonly used because it is relatively cheap tomanufacture and can be used to detect wavelengths in the visiblespectrum (i.e. visible light, 350 nm-800 nm). Traditional siliconmaterials require substantial path lengths and absorption depths todetect photons having wavelengths longer than approximately 700 nm.While visible light can be absorbed at relatively shallow depths insilicon, absorption of longer wavelengths (e.g. 900 nm) in silicon of astandard wafer depth (e.g. approximately 750 μm) is poor if at all.

SUMMARY

The present disclosure provides various systems and devices having aunique architecture that can determine distance and generate threedimensional representations of a subject, including associated methodsthereof. In one aspect, for example, an imaging system capable ofderiving three dimensional information from a three dimensional subjectis provided. Such a system can include a first imager array having afirst light incident surface and a second imager array having a secondlight incident surface. The second imager array can be coupled to thefirst imager array at a surface that is opposite the first lightincident surface, with the second light incident surface being orientedtoward the first imager array and at least substantially uniformlyspaced at a distance of from about 2 microns to about 150 microns fromthe first light incident surface. The system can also include a systemlens positioned to direct incident light along an optical pathway ontothe first light incident surface of the first imager. The first imagerarray is operable to detect a first portion of the light passing alongthe optical pathway and to pass through a second portion of the light,where the second imager array is operable to detect at least a part ofthe second portion of light. In one aspect, the first imager and thesecond imager are detecting and comparing light having substantially thesame wavelength in order to calculate distance to a subject or togenerate a three dimensional representation of the subject. Regardingthe frequencies of light that can be utilized by the present imagerarrays, the first portion of light and the second portion of light canhave at least one wavelength of from about 500 nm to about 1100 nm. Inanother aspect, the first portion of light and the second portion oflight can have at least one wavelength of from about 750 nm to about1100 nm. Additionally, in some aspects such a system can further includean active light emitter configured to emit active light radiation atleast substantially toward the three dimensional subject, where theactive light radiation has a center wavelength of from about 750 nm toabout 1100 nm. In another aspect, the active light radiation has acenter frequency of 850 nm, 940 nm, or 1064 nm.

In another aspect, the system can also include a computation moduleoperable to calculate distance data from the imaging system to the threedimensional subject using first image data collected by the first imagerarray from the first portion of light and second image data collected bythe second imager array from the second portion of light. In anotheraspect, the computation module is operable to generate a threedimensional representation of the three dimensional subject from thedistance data. Furthermore, in some aspects the imaging system can beincorporated into a computing system operable to alter computation basedon variations in distance data derived from movements of a subject.

Additionally, a variety of system configurations are contemplated, whichare considered to be non-limiting. In one aspect, the first imager arrayincludes a plurality of pixels architecturally configured as front-sideilluminated (FSI) pixels. In another aspect, the second imager arrayincludes a plurality of pixels architecturally configured as FSI pixelsor backside illuminated (BSI) pixels.

Furthermore, various structures can be utilized to redirect or otherwisereflect light that passes through the system back into the system. Inone aspect, a textured region can be coupled to the second imager arrayon a side opposite the first imager array, such that the textured regionis positioned to redirect light passing through the second imager arrayback into the second imager array. In another aspect, the system caninclude a reflector coupled to the second imager array on a sideopposite the first imager array, such that the reflector is positionedto reflect light passing through the second imager array back into thesecond imager array.

The present disclosure additionally provides a method of determiningdistance to a subject. Such a method can include focusing incident lightalong an optical pathway onto a first light incident surface of a firstimaging array, wherein the first imaging array captures a first portionof the light having at least one wavelength of from about 500 nm toabout 1100 nm to generate a first data set and passes through a secondportion of the light along the optical pathway. The method can alsoinclude receiving the second portion of the light onto a second lightincident surface of a second imaging array, wherein the second imagingarray captures the second portion of the light having at least onewavelength of from about 500 nm to about 1100 nm to generate a seconddata set. In another aspect, the first portion of the light has at leastone wavelength of from about 750 nm to about 1100 nm and the secondportion of the light has at least one wavelength of from about 750 nm toabout 1100 nm. Additionally, the distance to the subject can then bederived from variations between the first data set and the second dataset. In some aspects, at least part of the second portion of light thatpasses through the second imaging array can be redirected back into thesecond imaging array.

The distance between the first imaging array and the second imagingarray can vary depending on the wavelengths of light being utilized andthe distances to which three dimensional detection is desired. In oneaspect, however, the distance between the first light incident surfaceand the second light incident surface is from about 2 microns to about150 microns.

In some aspects the method can further include emitting active lightradiation toward the subject such that at least a portion of theincident light focused along the optical pathway includes the activelight radiation. In one aspect, the active light radiation can be IRlight radiation. In another aspect, the active light radiation can havea center frequency selected from 850 nm, 940 nm, and 1064 nm.

In yet another aspect the method can further include generating a threedimensional representation of the subject. In one specific aspect,generating the three dimensional representation can include determininga plurality of distances from the first light incident surface to asurface of the subject at a plurality of locations across the surface ofthe subject, and using the distances to generate the three dimensionalrepresentation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantage of the presentdisclosure, reference is being made to the following detaileddescription of various embodiments and in connection with theaccompanying drawings, in which:

FIG. 1 shows a cross sectional view of a stacked imager in accordancewith an aspect of the present disclosure.

FIG. 2 shows a schematic diagram of the effects of changing distance toa subject on a stacked imager system in accordance with another aspectof the present disclosure.

FIG. 3A shows a schematic diagram of the effects of changing distance toa subject on a stacked imager system in accordance with another aspectof the present disclosure.

FIG. 3B shows a schematic diagram of the effects of changing distance toa subject on a stacked imager system in accordance with another aspectof the present disclosure.

FIG. 3C shows a schematic diagram of the effects of changing distance toa subject on a stacked imager system in accordance with another aspectof the present disclosure.

FIG. 4 shows a cross sectional view of a stacked imager system inaccordance with an aspect of the present disclosure.

FIG. 5 shows a cross sectional view of a stacked imager system inaccordance with an aspect of the present disclosure.

FIG. 6A shows a cross sectional view of various steps in the manufactureof a stacked imager in accordance with another aspect of the presentdisclosure.

FIG. 6B shows a cross sectional view of various steps in the manufactureof a stacked imager in accordance with another aspect of the presentdisclosure.

FIG. 6C shows a cross sectional view of various steps in the manufactureof a stacked imager in accordance with another aspect of the presentdisclosure.

FIG. 6D shows a cross sectional view of various steps in the manufactureof a stacked imager in accordance with another aspect of the presentdisclosure.

FIG. 6E shows a cross sectional view of various steps in the manufactureof a stacked imager in accordance with another aspect of the presentdisclosure.

FIG. 7A shows a cross sectional view of various steps in the manufactureof a stacked imager in accordance with another aspect of the presentdisclosure.

FIG. 7B shows a cross sectional view of various steps in the manufactureof a stacked imager in accordance with another aspect of the presentdisclosure.

FIG. 7C shows a cross sectional view of various steps in the manufactureof a stacked imager in accordance with another aspect of the presentdisclosure.

FIG. 7D shows a cross sectional view of various steps in the manufactureof a stacked imager in accordance with another aspect of the presentdisclosure.

FIG. 7E shows a cross sectional view of various steps in the manufactureof a stacked imager in accordance with another aspect of the presentdisclosure.

DETAILED DESCRIPTION

Before the present disclosure is described herein, it is to beunderstood that this disclosure is not limited to the particularstructures, process steps, or materials disclosed herein, but isextended to equivalents thereof as would be recognized by thoseordinarily skilled in the relevant arts. It should also be understoodthat terminology employed herein is used for the purpose of describingparticular embodiments only and is not intended to be limiting.

Definitions

The following terminology will be used in accordance with thedefinitions set forth below.

It should be noted that, as used in this specification and the appendedclaims, the singular forms “a,” and, “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a dopant” includes one or more of such dopants andreference to “the layer” includes reference to one or more of suchlayers.

As used herein, the terms “textured region” and “textured surface” canbe used interchangeably, and refer to a surface having a topology withnano- to micron-sized surface variations formed by a texturingtechnique, a few examples of which are discussed herein. While thecharacteristics of such a surface can be variable depending on thematerials and techniques employed, in one aspect such a surface can beseveral hundred nanometers thick and made up of nanocrystallites (e.g.from about 10 to about 50 nanometers) and nanopores. In another aspect,such a surface can include micron-sized structures (e.g. about 2 μm toabout 10 μm). In yet another aspect, the surface can include nano-sizedand/or micron-sized structures from about 5 nm and about 10 μm. In yetanother aspect the surface features can be from about 100 nm to about 1μm.

As used herein, the terms “surface modifying” and “surface modification”refer to the altering of a surface of a semiconductor material to form atextured surface using a variety of surface modification techniques.Non-limiting examples of such techniques include plasma etching,reactive ion etching, porous silicon etching, lasing, chemical etching(e.g. anisotropic etching, isotropic etching), nanoimprinting, materialdeposition, selective epitaxial growth, shallow trench isolationtechniques, and the like, including combinations thereof.

As used herein, the term “subject” refers to any object, living ornon-living, that has a three dimensional structure or that can be imagedto determine distance. Non-limiting examples can include humans,animals, vehicles, buildings and building structures such as doors,windows, and the like, plants, animal enclosures, geological structures,and the like.

As used herein, the term “backside illumination” (BSI) refers to adevice architecture design whereby electromagnetic radiation is incidenton a surface of a semiconductor material that is opposite a surfacecontaining the device circuitry. In other words, electromagneticradiation is incident upon and passes through a semiconductor materialprior to contacting the device circuitry.

As used herein, the term “front side illumination” (FSI) refers to adevice architecture design whereby electromagnetic radiation is incidenton a surface of a semiconductor material containing the devicecircuitry. In some cases a lens can be used to focus incident light ontoan active absorbing region of the device while reducing the amount oflight that impinges the device circuitry.

As used herein, the term “light incident surface” refers to a surface ofan active semiconductor layer in an imager that is first struck by lightentering the imager. As such, other materials that make up an imager ora device containing an imager that are positioned between the incominglight and the active layer should not be considered to be light incidentsurfaces unless the context clearly indicates otherwise. In the case ofmultiple imagers stacked upon one another, each imager will have a lightincident surface. Distances described herein between light incidentsurfaces of stacked imagers, for example, represent the distancesbetween the active layer surfaces of each imager that is first struck byincident light on an initial pass through each imager.

In this application, “comprises,” “comprising,” “containing” and“having” and the like can have the meaning ascribed to them in U.S.Patent law and can mean “includes,” “including,” and the like, and aregenerally interpreted to be open ended terms. The terms “consisting of”or “consists of” are closed terms, and include only the components,structures, steps, or the like specifically listed in conjunction withsuch terms, as well as that which is in accordance with U.S. Patent law.“Consisting essentially of” or “consists essentially of” have themeaning generally ascribed to them by U.S. Patent law. In particular,such terms are generally closed terms, with the exception of allowinginclusion of additional items, materials, components, steps, orelements, that do not materially affect the basic and novelcharacteristics or function of the item(s) used in connection therewith.For example, trace elements present in a composition, but not affectingthe composition's nature or characteristics would be permissible ifpresent under the “consisting essentially of” language, even though notexpressly recited in a list of items following such terminology. Whenusing an open ended term, like “comprising” or “including,” it isunderstood that direct support should be afforded also to “consistingessentially of” language as well as “consisting of” language as ifstated explicitly, and vice versa. Further, it is to be understood thatthe listing of components, species, or the like in a group is done forthe sake of convenience and that such groups should be interpreted notonly in their entirety, but also as though each individual member of thegroup has been articulated separately and individually without the othermembers of the group unless the context dictates otherwise. This is trueof groups contained both in the specification and claims of thisapplication. Additionally, no individual member of a group should beconstrued as a de facto equivalent of any other member of the same groupsolely based on their presentation in a common group without indicationsto the contrary.

As used herein, the term “substantially” refers to the complete ornearly complete extent or degree of an action, characteristic, property,state, structure, item, or result. For example, an object that is“substantially” enclosed would mean that the object is either completelyenclosed or nearly completely enclosed. The exact allowable degree ofdeviation from absolute completeness may in some cases depend on thespecific context. However, generally speaking the nearness of completionwill be so as to have the same overall result as if absolute and totalcompletion were obtained. The use of “substantially” is equallyapplicable when used in a negative connotation to refer to the completeor near complete lack of an action, characteristic, property, state,structure, item, or result. For example, a composition that is“substantially free of” particles would either completely lackparticles, or so nearly completely lack particles that the effect wouldbe the same as if it completely lacked particles. In other words, acomposition that is “substantially free of” an ingredient or element maystill actually contain such item as long as there is no measurableeffect thereof.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 1 to about 5” should beinterpreted to include not only the explicitly recited values of about 1to about 5, but also include individual values and sub-ranges within theindicated range. Thus, included in this numerical range are individualvalues such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4,and from 3-5, etc., as well as 1, 2, 3, 4, and 5, individually.

This same principle applies to ranges reciting only one numerical valueas a minimum or a maximum. Furthermore, such an interpretation shouldapply regardless of the breadth of the range or the characteristicsbeing described.

The Disclosure

The present disclosure provides devices, systems, and methods forobtaining 3D information from an object. For example, in one aspect twoimager arrays can be positioned in a stacked configurations along anoptical axis, such that light passes through the first imager sensorhaving an array of pixels before contacting the second imager sensorhaving an array of pixels. Such an arrangement is shown schematically inFIG. 1. A first imager array 102 is positioned in a stackedconfiguration with a second imager array 104. The first imager array 102captures a first portion of the incident light 106, while the secondimager array 104 captures a second portion of the incident light 108that passes through the first imaging array. It is noted that, while theportions of light are shown as distinct lines in FIG. 1 for clarity,these lines are intended to represent the portion of the overallincident light that is absorbed by each imager array. Thus, light froman object that is being imaged is captured on both imager arrays andwill create different image patterns on each imager array that is afunction of the distance from each imager array to the object.Differences in these image patterns can thus be utilized to obtaindistance and/or 3D information about the object. In some cases a “lightfield” can be computed giving, for example, the light wavelength,intensity, and direction of light rays passing through the imager.Computations can then performed, in some cases in real time, by anon-chip processing unit or in a system processing unit to provide avariety of data, including visible image, IR image, range or distance tothe object, 3D information, and the like. The object distanceinformation collected can also be used to create a three dimensionalimage of the object.

FIG. 2 shows a side view schematic diagram of such three dimensionalimaging at different distances, represented by rows 1-5. The imagingdevice can include a first imager array 202, a second imager array 204,and a system lens 206 for focusing incident light 208 onto the first andsecond imager arrays. A subject 210 is shown at a given distance foreach of rows 1-5 from the imaging arrays. The boxes shown to the rightof the imager arrays represent the imaging surface of each of thearrays, with the imaging surface for the first imaging array 202 beingon the left and the imaging surface for the second imaging array 204being on the right. The circle shown in each of the imaging surfacesrepresents the image patterns formed on each imaging surface of thesubject 208 for a given distance. As is shown in FIG. 2, as the subjectmoves closer to the imager arrays, the dimensions of the image patternson the imaging surfaces change as a function of the distance to eachimager array. As such, the differences between the image patterns for agiven distance can be utilized to calculate the distance to the subject.As the image pattern differences change, the change in distance to thesubject can be repeatedly calculated. Furthermore, three dimensionalrepresentations can be obtained of subjects, including for subjects withcomplex surface contours or structures. In such cases, the threedimensional nature of a subject is reflected in the image patterncreated on each of the imager arrays. The differences between imagepatterns from each array can be utilized to create a three dimensionalrepresentation. Such a representation can include three dimensionalmeasurements of the subject, as well as three dimensional images.

These concepts are further illustrated in FIGS. 3A-C where incidentlight 302 is shown passing through a first imager array 304 and a secondimager array 306. The incident light 302 contacts the first imager array304 with a first image pattern 308 that is related, at least in part, tothe distance to the subject and the characteristics and distance of thesystem lens (not shown) from the first imager array 302. Due to thegreater distance of the subject and the system lens from the secondimager array 306, the second image pattern 310 is different from thefirst image pattern 308. For example, the patterns will often differ insize between the two arrays, and the pixels that detect the pattern willbe different between the two imager arrays. It is noted, however, thatin some limited situations the patterns on both imager arrays will bethe same size. As the subject moves closer to the imager arrays (FIGS.3B and 3C), the first and second image patterns concomitantly vary.

The following are exemplary descriptions of techniques that can beutilized to perform such stacked imager array calculations. It should beunderstood that these techniques are non-limiting, and that the scope ofthe present disclosure includes any technique for performing suchcalculations. Accordingly, the distance to a subject can be calculatedbased on the image feature difference between the first image patternand the second image pattern of the stacked imager array, with knownimager stack structure and system lens data.

In one aspect, distance to a subject with a point or near-point sourceas well as image features can be calculated directly. Such point ornear-point sources will generally produce simple image patters on eachimager array. First, the effective image pattern radii of the firstimage pattern and the second image pattern can be determined as r1 andr2, respectively. The effective feature radii of a defocussed image canbe calculated from the total volume of the image pixel values accordingto Equations I and II:

r1=sqrt(sum(pixel_value_image1)/(pi*max(pixel_value_image1)   I

r2=sqrt(sum(pixel_value_image2)/(pi*max(pixel_value_image2)   II

where r1 and r2 are the image radii of the first image pattern and thesecond image pattern. Pixel values are in the sampling kernels of 5×5 to10×10 pixels. Optically, with generic imaging system optics, focusedimages occur at a single plane with the best focal distance relative tothe optics for specific subject. At this best focused location, theimage is the sharpest with the smallest feature size for any imagecontents. At any other location, image will be defocused (a blurredimage), with feature sizes that are bigger for the same image content atfocused location.

Next, the smallest image size location from the first image based on thefeature radii of the first image pattern and the second image pattern iscalculated by Equation III:

d=r1*t/(r1+r2)   III

where d is the distance from the first image, r1 and r2 are theeffective feature radii of the first image and second image, and t isthe separation between the first light incident surface and second lightincident surface. The smallest image feature size location is at thebest focus location, where image is focused with minimum blur. Dependingon the design of the system, for some aspects including a mix of frontside illuminated and back side illuminated imagers, an offset may beintroduced to compensate for the difference in the distance from thefront of the image array to the effective image plane.

The subject distance can then be calculated using the lens imagingEquation IV:

D=1/(1/f−1/(s+d))   IV

where D is the distance from the subject to the lens' principle plane, fis the focal length of the imaging lens, s is the distance from lensprinciple plane to the first image, and d is the distance from the firstimage to the smallest image location. In some aspects the actualdistance calculation can consider the image stack layer materialrefractive index because the actual distance in the non-air materialwill be, according to Equation V:

(Distance in material)=(distance in air)*(material refractive index)   V

Furthermore, the x and y position of an image feature in an imager arrayused in distance calculation can be calculated using a centroid, as isshown by Equations VI and VII:

xc=sum(x*(pixel value))/sum(pixel value)   VI

yc=sum(y*(pixel value))/sum(pixel value)   VII

It is noted that the centroid xc and yc position is not limited by thepixel resolution, as x and y are pixel coordinates. Sub-pixel result canbe used to achieve required calculation precision. The precision of theposition can be sensor signal-to-noise ratio limited.

For a non-point object source, image feature size can be determined bycross correlation between the inverse scaled first image and secondimage. First, the inverse scaled cross correlation is calculatedaccording to Equation VIII:

C=sum((Inverse scaled first image pixel values)*(second image pixelvalue))   VIII

where C is the result of the inverse scaled correlation. The inversescaled first image is processed by applying the inverse scale factor kto the image size (similar to a digital zoom). Again, the scaling is notpixel resolution limited, and sub-pixel scaling process is used to findthe best correlated scale factor k with the highest correction result C.

The best correlated scale factor k can then be used to describe therelationship between the first image and the second image. The imagedistance from the first image than can be calculated as according toEquation IX:

d=r1*t/(r1+r2)32 r1*t/(r1+k*r1)=t/(1+k)   IX

where d is the image distance from first image to the smallest imagesize location, t is the separation between first light incident surfaceand second light incident surface, and k is the scale factor applied tothe first image in cross correlation. Depending on the design of thesystem, for some aspects including a mix of front side illuminated andback side illuminated imagers, an offset may be introduced to compensatefor the difference in the distance from the front of the image array tothe effective image plane.

The distance to the subject can then be calculated according to EquationX:

D=1/(1/f−1/(s+d))   X

where D is the distance from the subject to the lens principle plane, fis the focal length of the imaging lens, s is the distance from lensprinciple plane to the first image, and d is the distance from firstimage to the smallest image location. Again, compensation can be madefor the refractive index of the imager array material.

A variety of configurations are contemplated for carrying out thecalculations utilized to derive distance and/or three dimensionalinformation from a subject. For example, in one aspect the calculationsor at least a portion of the calculations can be performed on-chip withthe imager arrays. In another aspect, a dedicated image processing unitcan be utilized for the calculations or at least a portion of thecalculations. In other aspects, the calculations or at least a portionof the calculations can be performed in a computing device.

Turning to various physical configurations of the system, in one aspectan imaging system capable of deriving three dimensional information froma three dimensional subject can, as is shown in FIG. 4, include a firstimager array 402 having a first light incident surface 404 and a secondimager array 406 having a second light incident surface 408. The secondimager array 406 is coupled to the first imager array 402 at a surfacethat is opposite the first light incident surface 404. It is noted thatin one aspect the first imager array can be physically coupled to thesecond imager array. In another aspect, the first imager array can beoptically coupled to the second imager array. Furthermore, the secondlight incident surface 408 is oriented toward the first imager array 402and at least substantially uniformly spaced at a distance of from about2 microns to about 150 microns from the first light incident surface.The system can additionally include a system lens 410 positioned todirect incident light 412 along an optical pathway 414 onto the firstlight incident surface 404. In some aspects, the system lens 410 canhave a focal point 416 located in between the first light incidentsurface 404 and the second light incident surface 408, and/or in betweenthe first imager array 402 and the second imager array 406. The firstimager array 402 is operable to detect a first portion of the lightpassing along the optical pathway 414 and to pass through a secondportion of the light, and the second imager array 406 is operable todetect at least a part of the second portion of light. In some aspectsthe first portion of light and the second portion of light have at leastone wavelength of from about 500 nm to about 1100 nm. In another aspect,the first portion of light and the second portion of light have at leastone wavelength of from about 750 nm to about 1100 nm. In another aspect,the second portion of light includes at least substantially allwavelengths of light of from about 750 nm to about 1100 nm. In a furtheraspect, the first portion of light and the second portion of light havea center wavelength frequency between about 500 nm and about 1100 nm. Inanother aspect, the first portion of light and the second portion oflight have a center wavelength frequency between about 750 nm and about1100 nm.

The wavelengths of light utilized by the stacked imager system can varydepending on, among other things, the design of the system and theintended application. In some aspects the same or substantially the samelight wavelengths can be utilized by both the first imager array and thesecond imager array to derive distance and/or three dimensionalinformation from the subject. In other aspects, different lightwavelengths can be utilized by the first imager array than by the secondimager array. While in many aspects IR light wavelengths are used tocalculate three dimensional information about a subject, in some aspectsvisible light can be used to make such calculations. For example,assuming crystalline silicon imagers are utilized for the imager arrays,light in the visible spectrum of from about 500 nm to about 700 nm canbe used, provided the first imaging array is sufficiently thin to allowa second portion of the visible light to pass there through.Furthermore, in some cases different wavelengths of light can beutilized differently in the system. For example, infrared light can beused by both the first imager array and the second imager array togenerate a three dimensional representation or three dimensional image,while visible light can be captured by the first imager array in orderto generate a visible image of the subject. When the two representationsare combined, a resulting three dimensional visible image of the subjectcan be achieved.

In another aspect, system can include an active illumination source, afirst imager capable of detecting visible and infrared (IR) light and asecond imager capable of detecting IR light. The system can furtherinclude an active illumination source capable of emitting IR light. Theactive illumination source, first imager and the second imager canpulsed at the same frequency such that the pulsed IR light is detectedduring the pulse window. When the IR illumination source is off (i.e. inbetween pulses), the first image sensor is detecting and reading outvisible light data.

Additionally, in some aspects the one or more of the first and secondimager arrays can include light filters that are capable of filteringout specific wavelengths of light or ranges of wavelengths of light. Assuch, light having a certain wavelength or wavelength range can beconcentrated by a structure such as a system lens on a specific imagerarray or even a portion of an imager array. In one aspect, an IR cutfilter (moveable) or notch filter can be employed in front one or morepixels of the first imager array. Such a filter can pass infrared lightthat will be used in range or distance determination and filter outlight in the visible range. In some cases a long-pass filter can passboth infrared and visible red light. Similarly, a long-pass filter canbe utilized that passes green, red, and infrared light. In otheraspects, a band-pass filter can be used that passes visible light andspecific wavelengths of IR light, such as, for example, 850 nm, 940 nm,and/or 1064 nm light, while blocking all other wavelengths.

It is additionally contemplated that in one aspect the system caninclude a focusing system for altering the focal plane(s) of the imagingsystem. While various techniques are contemplated, in one aspect thedistance of the first imager array from the second imager array can bevaried by, for example, piezoelectric materials.

In some aspects, the system can additionally include an active lightemitter configured to emit active light radiation at least substantiallytoward the subject. While any light can be utilized as an active lightsource, in one aspect the active light source can emit light having acenter wavelength in the infrared range. In another aspect, the emittedlight can have a center wavelength of from about 750 nm to about 1100nm. In yet another aspect, the active light radiation can have a centerfrequency selected from 850 nm, 940 nm, 1064 nm, or a combinationthereof.

As has been described, in some aspects the system can include acomputational module that is operable to calculate distance data fromthe imaging system to the three dimensional subject using first imagedata collected by the first imager array from the first portion of lightand second image data collected by the second imager array from thesecond portion of light. Computational modules are well known, and caninclude various processing units, data storage, memory, I/Ofunctionality, and the like. In one aspect the computation module iscapable of generating a three dimensional representation of the subjectfrom the distance data. In another aspect the computational module cangenerate a three dimensional image from the data derived from the firstimager array and the second imager array. In other aspects, the imagingsystem can be incorporated into a computing system operable to altercomputation based on variations in distance data derived from movementsof a subject. For example, in the case of a human subject, motions madeby the subject can be captured by the imaging system and used by thecomputing system to alter the computation of the computing system. Inthe case of non-living subjects, computation of the computing system canbe varied according to the motion of an oncoming vehicle or other movingsubject.

Returning to the imager system configuration, in one aspect the distancefrom the first light incident surface to the second light incidentsurface is from about 1 microns to about 150 microns. In another aspect,aspect the distance from the first light incident surface to the secondlight incident surface is from about 10 microns to about 100 microns. Ina further aspect, the distance from the first light incident surface tothe second light incident surface is from about 1 micron to about 50microns. Furthermore, each of the first and second imager array is madeup of a plurality of pixels. The pixels can be architecturallyconfigured as front-side illuminated pixels or back-side illuminatedpixels. For example, in one aspect all of the first imager array pixelsand the second imager array pixels can be front-side illuminated pixels.In another aspect, all of the first imager array pixels can befront-side illuminated and all of the second imager array pixels can bebackside illuminated pixels. Additionally, it is contemplated that insome aspects either of the first or second imager arrays can befront-side illuminated while the other imager array can be backsideilluminated.

Furthermore, as is shown in FIG. 5, in some aspects a system can includea texture region 502 coupled to the second imager array 406 on a sideopposite the first imager array 402. In this case, the textured region502 is positioned to redirect light passing through the second imagerarray 406 back into the second imager array 406. The light passingthrough the second imager array is shown at 504, and the lightredirected back into the imager array is shown at 506. It is noted thatthe textured region 502 can be formed across all or substantially all ofthe back surface of the second imager array 406, or the textured region502 can be formed on a portion thereof. Additionally, in some aspectsthe textured region can be formed at the level of the pixels that makeup the imager array, and as such, can be formed on a portion of thepixel surface, substantially all of the pixel surface, or all of thepixel surface. Also, it is noted that callout numbers used in FIG. 5from previous figures denote the same or similar structures as theprevious figure. Furthermore, in some aspects a textured region isexplicitly disclaimed from being applied to the first imager array,while in other aspects such a textured region can be utilized.

The textured region can function to diffuse electromagnetic radiation,to redirect electromagnetic radiation, and/or to absorb electromagneticradiation, thus increasing the efficiency of the second imager array.The textured region can include surface features to thus increase theoptical path length of the second imager array. Such surface featurescan be micron-sized and/or nano-sized, and can be any shape orconfigurations. Non-limiting examples of such shapes and configurationsinclude cones, pillars, pyramids, micolenses, quantum dots, invertedfeatures, gratings, protrusions, and the like, including combinationsthereof. Additionally, factors such as manipulating the feature sizes,dimensions, material type, dopant profiles, texture location, etc. canallow the diffusing region to be tunable for a specific wavelength orwavelength range. Thus in one aspect, tuning the device can allowspecific wavelengths or ranges of wavelengths to be absorbed.

As has been described, textured regions according to aspects of thepresent disclosure can also allow an imager array to experience multiplepasses of incident electromagnetic radiation within the device,particularly at longer wavelengths (i.e. infrared). Such internalreflection increases the optical path length to be greater than thethickness of the semiconductor. This increase in the optical path lengthincreases the quantum efficiency of the device, leading to an improvedsignal to noise ratio.

The textured region can be formed by various techniques, includingplasma etching, reactive ion etching, porous silicon etching, lasing,chemical etching (e.g. anisotropic etching, isotropic etching),nanoimprinting, material deposition, selective epitaxial growth, shallowtrench isolation, and the like. One effective method of producing atextured region is through laser processing. Such laser processingallows discrete locations of the imager array or other substrate to betextured. A variety of techniques of laser processing to form a texturedregion are contemplated, and any technique capable of forming such aregion should be considered to be within the present scope. Examples ofsuch processing have been described in further detail in U.S. Pat. Nos.7,057,256, 7,354,792 and 7,442,629, which are incorporated herein byreference in their entireties. Briefly, a surface of a substratematerial is irradiated with laser radiation to form a textured orsurface modified region.

The type of laser radiation used to surface modify a material can varydepending on the material and the intended modification. Any laserradiation known in the art can be used with the devices and methods ofthe present disclosure. There are a number of laser characteristics,however, that can affect the texturing process and/or the resultingproduct including, but not limited to the wavelength of the laserradiation, pulse width, pulse fluence, pulse frequency, polarization,laser propagation direction relative to the semiconductor material, etc.In one aspect, a laser can be configured to provide pulsatile lasing ofa material. A short-pulsed laser is one capable of producingfemtosecond, picosecond and/or nanosecond pulse durations. Laser pulsescan have a central wavelength in a range of about from about 10 nm toabout 8 μm, and more specifically from about 200 nm to about 1200 nm.The pulse width of the laser radiation can be in a range of from abouttens of femtoseconds to about hundreds of nanoseconds. In one aspect,laser pulse widths can be in the range of from about 50 femtoseconds toabout 50 picoseconds. In another aspect, laser pulse widths can be inthe range of from about 50 picoseconds to 100 nanoseconds. In anotheraspect, laser pulse widths are in the range of from about 50 to 500femtoseconds. In another aspect, laser pulse widths are in the range offrom about 10 femtoseconds to about 500 picoseconds.

The number of laser pulses irradiating a target region can be in a rangeof from about 1 to about 2000. In one aspect, the number of laser pulsesirradiating a target region can be from about 2 to about 1000. Further,the repetition rate or frequency of the pulses can be selected to be ina range of from about 10 Hz to about 10 μHz, or in a range of from about1 kHz to about 1 MHz, or in a range from about 10 Hz to about 1 kHz.Moreover, the fluence of each laser pulse can be in a range of fromabout 1 kJ/m² to about 20 kJ/m², or in a range of from about 3 kJ/m² toabout 8 kJ/m².

In another aspect of the present disclosure, an imaging system canfurther include a reflector coupled to the second imager array on a sideopposite the first imager array. The reflector can be positioned toreflect light passing through the second imager array back into thesecond imager array. Numerous reflector materials are contemplated, andcan include any material or composite of materials that can function toreflect light. Non-limiting examples of such materials can includemetals, metal alloys, ceramics, polymers, glass, quartz, Bragg-typereflectors, and the like.

FIGS. 6A-E show various steps in the non-limiting manufacture of astacked imager structure according to one aspect of the presentdisclosure. As is shown in FIG. 6A, for example, first imager array 602is formed on the front side of a semiconductor layer 604. The firstimager array 602 can include any form of imager array that can beincorporated into an imager system, and any such device is considered tobe within the present scope. A variety of semiconductor materials arecontemplated for use as the semiconductor layer of the devices andmethods according to aspects of the present disclosure. As such, anysemiconductor material that can be used in a stacked imager device isconsidered to be within the present scope. Non-limiting examples of suchsemiconductor materials can include group IV materials, compounds andalloys comprised of materials from groups II and VI, compounds andalloys comprised of materials from groups III and V, and combinationsthereof. More specifically, exemplary group IV materials can includesilicon, carbon (e.g. diamond), germanium, and combinations thereof.Various exemplary combinations of group IV materials can include siliconcarbide (SiC) and silicon germanium (SiGe). In one specific aspect, thesemiconductor material can be silicon. In another specific aspect, thesemiconductor layer can be a silicon wafer. The silicon wafer/materialcan be monocrystalline, multicrystalline, microcrystalline, amorphous,and the like. In one specific aspect, the silicon material can be amonocrystalline silicon wafer.

Turning to FIG. 6B, a carrier substrate (or handle) 606 can be bonded tothe first imager array 602. Note that in FIG. 6B, the device has beenflipped or rotated 180° as compared to FIG. 6A. The carrier substratecan include a variety of materials. Because in many aspects the carriersubstrate 606 is a temporary substrate to be removed at a laterprocessing step, the material can be chosen based on its usefulness as atemporary substrate. It can also be beneficial for the carrier substrate606 to be capable of adequately holding the first imager array 602during processing of the semiconductor layer 604 and yet be capable ofeasy removal. Non-limiting examples of potential carrier substratematerials can include glass, ceramics, semiconductors, and the like,including combinations thereof.

Various bonding techniques are contemplated for attaching the carriersubstrate 606 to the first imager array 602, and any such bondingtechnique useful in making a stacked imager device is considered to bewithin the present scope. One such process can include a liquid UVcurable adhesive process that utilizes solids acrylic adhesives designedfor temporary bonding of semiconductor wafers to a glass carriersubstrate. This technique provides a rigid, uniform support surface thatminimizes stress on the wafer during the subsequent processing steps,resulting in less warpage, cracking, edge chipping and higher yields.Other exemplary methods can include bonding and detaching a temporarycarrier used for handling a wafer during the fabrication ofsemiconductor devices, includes bonding the wafer onto the carrierthrough an adhesive layer. After detaching the carrier from the wafer,the first adhesive layer remaining on the wafer is removed. In anothermethod, bonding at low or room temperature can include surface cleaningand activation by cleaning or etching, followed by polishing thesurfaces to be bonded to a high degree of smoothness and planarity.Reactive ion etching or wet etching is used to slightly etch thesurfaces being bonded. The etched surfaces may be rinsed in solutionssuch as ammonium hydroxide or ammonium fluoride to promote the formationof desired bonding species on the surfaces.

In one aspect, the first imager array 602 and the carrier substrate 606can be bonded at room temperature and a thermal treatment can be appliedto consolidate the bonding interface. The parameters of theconsolidation annealing can be controlled to provide a bonding energyhigh enough for the heterostructure to withstand post-bondingconventional process steps (e.g. CMOS processing). In one specificaspect, the bonding technique can include various oxide-oxide,oxide-silicon, or metal-metal bonding methods.

Some bonding processes can achieve a bond strength of at least 1 J/m² atroom temperature. For even higher bond strengths, a bake cycle at100°-300° C. can be utilized. Some of these oxide-oxide bonding processhave been described in U.S. Pat. No. 7,871,898 and U.S. Pat. No.5,843,832, which are incorporated by reference in their entireties. Onemethod of direct bonding a silicon wafer onto an insulated wafer inorder to obtain a stacked imager device is similar to the bonding of twosilicon wafers together, with the exception that before bonding a thinthermal oxide layer (e.g. about 1 micron) is grown on one of the wafers.

Release of the carrier substrate from the device layer can varydepending on the attachment process. Acrylic adhesives, for example, canbe released by exposure to UV light. More permanent bonds, such assilicon-oxide bonds may require the removal of the carrier substrate bymechanical grinding and/or chemical etching to expose the device layer.

Turning to FIG. 6C, the semiconductor layer 604 (FIG. 6B) is at leastpartially removed (e.g. polished and thinned) to expose the backside ofthe first imager array 602 or, in other words, to form a processedsurface 608 at the backside of the first imager array 602. Thus, theresulting structure is comprised of the first substrate 606 coupled tothe first imager array 602. At this point, any necessary or beneficialbackside processing can be performed on the processed surface 608 of thefirst imager array 602. Such beneficial backside processing can include,without limitation, shallow or deep trench formation, via formation,annealing, implantation, and the like.

In one aspect, backside processing can also include exposing contactpads associated with the first imager array. By opening the backside ofthe device layer (i.e. at the processed surface), such electricalcontacts can be exposed for bonding and providing electrical contact tosubsequent structures, such as the second imager array (see below).Opening the backside can occur by any known technique, including thethinning and processing methods described. In one specific aspect,opening the backside can be accomplished via plasma etching.

Any technique useful for removing the semiconductor layer 604 isconsidered to be within the present scope. Non-limiting examples caninclude ion implantation/separation processes, laser ablation, lasersplitting, CMP processing, dry etching, wet etching and the like,including combinations thereof. In one specific aspect, thesemiconductor layer is removed by CMP techniques to expose the devicelayer 602.

Following removal or thinning of the semiconductor layer 604, a secondimager array 610 is bonded to the backside of the first imager array602, as is shown in FIG. 6D. Note that in FIG. 6D, the device has beenflipped or rotated by 180° compared to FIG. 6C. Any bonding techniquecan be utilized to bond the second imager array 210 to the first imagerarray 202, as was described for the bonding of the first substrate 206to the first imager array 202 (FIG. 6B), provided the process iscompatible with both structures. It is noted that any spacing thatexists between the first and second imager arrays can be filled with alight transparent material such as amorphous silicon, an oxide, nitride,or the like. In some aspects an air gap can be maintained between thefirst and second imager arrays. Such a gap can be filled with actualair, an inert gas, a vacuum, etc.

Additionally, it is noted that the first imager array and the secondimager array can be electrically coupled to, and thus can function inconjunction with, one another. Such electrical coupling can beaccomplished by vias formed through the processed surface that connectthe two imager arrays.

Turning to FIG. 6E, in some aspects the carrier substrate 606 (FIG. 6D)can be removed from the first imager array 602 following bonding of thesecond imager array 610. Thus, the resulting stacked imager structureshown in FIG. 6E includes a second imager array 610 bonded to a firstimager array 602.

In another aspect, FIGS. 7A-E show various steps in the manufacture of astacked imager device using an embedded oxide layer to facilitatethinning and creating a space between the imager arrays. As is shown inFIG. 7A, for example, first imager array 702 can be formed on the frontside of a semiconductor layer 704. The first imager array 702 caninclude any form of imager array that can be incorporated into a stackedimager device, as has been described. A thin oxide layer 703 can beembedded within the semiconductor layer 704, either before or after theformation of the first imager array 702. The thin oxide layer can be ofany shape and thickness useful for the particular device design. In someaspects, however, the thin oxide layer can be from about 4000 angstromsto about 1.5 microns thick. It is also noted that commercial SOIsubstrates can be used that are manufactured having such a thin oxidelayer embedded. Turning to FIG. 7B, a carrier substrate 706 can bebonded to the first imager array 702. Note that in FIG. 7B, the devicehas been flipped or rotated 180° as compared to FIG. 7A. The carriersubstrate can include a variety of materials. Because in most aspectsthe carrier substrate 706 is a temporary substrate to be removed at alater processing step, the material can be chosen based on itsusefulness as a temporary substrate.

Turning to FIG. 7C, the semiconductor layer 704 (FIG. 7B) is at leastpartially removed to form a processed surface 708 near the backside ofthe first imager array 702. In one aspect, the semiconductor layer 704can be removed at least to the thin oxide layer 703. In some aspects atleast a portion of the thin oxide layer can remain, while in otheraspects the thin oxide layer can be completely removed from thesemiconductor layer. This material can be removed by any known method,such as, for example, laser splitting, polishing, thinning, etching,lapping or grinding, CMP processing, or a combination thereof.

Thus, the resulting structure is comprised of the carrier substrate 706coupled to the first imager array 702. A portion of the semiconductorlayer 704 can remain coupled to the first imager array 702 opposite thecarrier substrate 706. At this point, any necessary or beneficialbackside processing can be performed on the first imager array 702. Inone specific aspect, processing the semiconductor layer on the backsidecan include implant and/or laser anneal conditions to reduce surfacedefects.

Following thinning of the semiconductor layer 704, a second imager array710 can be bonded to the semiconductor layer 704 at backside of thefirst imager array 702, as is shown in FIG. 7D. Note that in FIG. 7D,the device has been flipped or rotated 180° compared to FIG. 7C. Anybonding technique can be utilized to bond the second imager array 710 tothe semiconductor layer 704, as has been described.

Turning to FIG. 7E, in some aspects the carrier substrate 706 (FIG. 7D)can be removed from the first imager array 702 following bonding of thesecond imager array 710. Thus, the resulting stacked imager structureshown in FIG. 7E includes a second imager array 710 bonded to thesemiconductor layer 704, which is bonded to the first imager array 702.It is noted that the distance between the imagers can be varied duringmanufacture by varying the thickness of the semiconductor layer 704 thatremains and is bonded between the imager arrays.

The present disclosure additionally provides methods of determiningdistance to a subject. In one aspect, for example, such a method caninclude focusing incident light along an optical pathway onto a firstlight incident surface of a first imaging array, where the first imagingarray captures a first portion of the light having at least onewavelength of from about 500 nm to about 1100 nm to generate a firstdata set and passes through a second portion of the light along theoptical pathway. The method can also include receiving the secondportion of the light onto a second light incident surface of a secondimaging array, where the second imaging array captures the secondportion of the light having at least one wavelength of from about 500 nmto about 1100 nm to generate a second data set. Furthermore, thedistance to the subject can be derived from variations between the firstdata set and the second data set. In another aspect the method can alsoinclude redirecting at least part of the second portion of the lightthat passes through the second imaging array back into the secondimaging array.

In another aspect, the present disclosure provides an imaging systemcapable of deriving three dimensional information from a threedimensional subject. Such a system can include an active illuminationsource capable of emitting pulsed infrared light, a first imager capableof detecting visible and infrared light, and a second imager capable ofdetecting infrared light. The active illumination source, first imager,and the second imager can be pulsed at a frequency and duty cycle suchthat the pulsed infrared light is detected by the first imager and thesecond imager when the active illumination is on. In one aspect thefirst imager is operable to detect visible light when the activeillumination source is in an off state.

It is to be understood that the above-described arrangements are onlyillustrative of the application of the principles of the presentdisclosure. Numerous modifications and alternative arrangements may bedevised by those skilled in the art without departing from the spiritand scope of the present disclosure and the appended claims are intendedto cover such modifications and arrangements. Thus, while the presentdisclosure has been described above with particularity and detail inconnection with what is presently deemed to be the most practicalembodiments of the disclosure, it will be apparent to those of ordinaryskill in the art that numerous modifications, including, but not limitedto, variations in size, materials, shape, form, function and manner ofoperation, assembly and use may be made without departing from theprinciples and concepts set forth herein.

1-24. (canceled)
 25. An imaging system capable of deriving threedimensional information from a three dimensional subject, comprising: anactive illumination source capable of emitting pulsed infrared light; afirst imager capable of detecting visible and infrared light; a secondimager capable of detecting infrared light, wherein the activeillumination source, first imager, and the second imager are pulsed at afrequency and duty cycle such that the pulsed infrared light is detectedby the first imager and the second imager when the active illuminationis on.
 26. The imaging system of claim 25, wherein the first imager isoperable to detect visible light when the active illumination source isin an off state.